The present application relates to a non-aqueous electrolyte battery having enhanced input and output characteristics of a positive electrode and a positive electrode and to a method for manufacturing the same.
Among non-aqueous electrolyte batteries, a lithium ion secondary battery is rapidly developing as a power source of portable electronic devices such as a mobile phone and a personal computer. In the power source for such a portable electronic device, an energy density, namely an energy storage capacity per unit volume is the most necessary characteristic, and how long the portable electronic device can be used attracts interest. As to a negative electrode material of the lithium ion secondary battery, realization of a high density of the electrode using a carbon material of every sort has been developed. In all of the cases, it is aimed to enhance the energy density or cycle characteristics.
In the lithium ion secondary battery, when polyvinylidene fluoride with excellent lithium ion mobility is used as a negative electrode binder, input and output characteristics of the battery can be enhanced.
However, in discharging at a large current, the lithium ion mobility in polyvinylidene fluoride is limited. Therefore, there were involved problems that polyvinylidene fluoride which covers the surface of a positive electrode active material impairs an interfacial reaction; that the voltage is lowered due to the influence of a resisting component; and that the output of the battery is decreased. In the light of the above, the overvoltage is largely applied in the positive electrode, resulting in an enormous lowering of cycle characteristics. Consequently, it has been difficult to increase the thickness of the active material layer or to increase the volume density. Accordingly, for the purpose of obtaining a high-output battery, it is effective and important to reduce the ionic resistance in polyvinylidene fluoride.
On the other hand, there is proposed a positive electrode active material in which aluminum oxide is coated on a part of the surface of a particle of lithium cobaltate as a lithium cobalt complex oxide (see JP-A-2002-151077). Here, a positive electrode active material in which aluminum oxide is coated in a proportion of from 1 to 4% by mole relative to cobalt in a lithium cobaltate particle powder is obtained by adding an aluminum salt in an aqueous solution having a lithium cobaltate particle dispersed therein, regulating a pH of the solution to adsorb a fine aluminum hydroxide colloid on the surface of the lithium cobaltate particle and then heat treating this lithium cobaltate particle in an oxidative atmosphere of from 600 to 900° C. In a non-aqueous electrolyte secondary battery using such a positive electrode active material, it is recognized that an oxidation decomposition reaction between tetravalent cobalt on the surface area of the positive electrode active material particle and an electrolytic solution, which is expected to occur at the time of a high temperature or under a high charge voltage of 4.8 V or more, can be suppressed.